A traditional metal wire strain gauge or foil type strain gauge is limited in measuring large strain since they typically only measure strain up to around several percent. For example, platinum-8% tungsten has the strain range of about ±0.3%. A copper-nickel alloy has the strain range of up to ±5%.
A strain sensor made of commercial fabrics coated by a conductive polymer is able to detect a large strain deformation; however, the repeatability and reliability is limited. After frequent usage, the performance of this strain sensor reduces gradually due to the poor mechanical properties of the polymer, the aging of polymer and reduction of adhesion, especially in cyclic deformation.
A salt water based strain sensor is able to measure large strain and has no aging problem. However, the evaporation of water and the corrosion of the electrodes are significant problems encountered.
Mercury based strain sensors are able to measure large strain. However, the use of mercury is not environmentally friendly.
Accordingly, there is a desire for a strain sensor that ameliorates at least some of the problems identified with prior art strain gauges outlined above.